根据对话内容及方框中所给的句子补全对话.其中有一多余的. A. Have you cleaned the windows yet? B. Have you cleaned the blackboard yet? C. Who is on duty today? D. Have you carried some water yet? E. Have you watered the flowers? F. When did you do it? A: Good morning.  Xiao Jing. __ 1 __. B: I am.  Mr Zhang. A: __ 2 __. B: Yes, I cleaned it ten minutes ago. A: __ 3 __. B: Yes, I did it half an hour ago. A: __ 4 __. B: Yes. Look, they are as clean as mirrors. A: So they are! __ 5 __. B: Yes, some boys helped me to get water from the well. A: Very good, thank you, Xiang Jing.  Now, let's begin our class.